The present invention relates to a thermostat failure diagnosis apparatus for an internal combustion engine, which diagnoses presence of a thermostat for performing temperature adjustment of cooling water of the internal combustion engine.
In an internal combustion engine mounted on an automobile (vehicle), for example, a radiation, of a water-cooled engine, having an introducing/discharging water passages is coupled to a water jacket formed inside of an engine body such that it surrounds a combustion chamber and a cylinder, and cooling water is made to circulate within the water jacket, so that heat of the engine is radiated to the air.
In such an engine, in order to always keep a cooling water temperature suitable, an automatic opening/closing thermostat for opening/closing of a cooling water passage in accordance with the cooling water temperature is provided at the cooling water passage of the engine, for example, at an outlet of the water jacket.
Since the thermostat generally adopts a structure to open/close a valve by a volume change of wax paraffin, it is excellent in durability, nevertheless it can break down.
Although a failure where the thermostat does not open but remains closed can be inferred from behavior that a needle of a water temperature meter in an instrument panel of an automobile abruptly rises, a failure where the thermostat does not close but remains opened is hard to recognize.
As a technique of diagnosing the failure of the thermostat where it remains opened, a technique of failure diagnosis of a thermostat is recently proposed in Japanese Patent Unexamined Publication No. H10-184433.
This failure diagnosis is a technique in which judgment is made on either one of an elapsed time in which a rising quantity in cooling water temperature at an engine side reaches a predetermined value after starting of an engine, or the cooling water temperature at the engine side reaches a predetermined temperature, the number of times of ignition, and an integrated value of quantity of heat generated from the engine, and the opening failure of the thermostat is diagnosed on the basis of the judgment value.
By the way, an automobile is used in various ways, for example, an idling operation is performed after starting of an engine, or made to run immediately after starting of an engine, and usually, the idling operation is often performed after starting of an engine.
However, in the failure diagnosis of the above publication, when the idling operation is performed after starting of an engine, there is a fear that such an erroneous diagnosis is made that the thermostat has broken down though it has not actually broken down.
That is, in the idling operation of an engine, as compared with the case where an automobile is running, since the quantity of generated heat of the engine is low, the greater part of the quantity of the generated heat is released into the air, the quantity of heat transmitted from the engine to cooling water becomes low, and it takes time for the temperature of the cooling water temperature to rise.
Thus, when the failure diagnosis disclosed in the above publication is carried out in the state where the idling is continued after starting of the engine, since the quantity of heat transmitted from the engine to the cooling water is low, even if either one of the elapsed time after starting of the engine, the number of times of ignition, and the engine generating heat quantity is integrated, an integrated value required for failure judgment can not be obtained, and it is apt to make an erroneous judgment that the thermostat has broken down though it is not normal. Particularly, such a state is apt to occur in a cold district or at a low outside air temperature since the greater part of the heat quantity is lost to keep the engine temperature and the heat quantity contributing to the rising of cooling water temperature becomes extremely low.
The present invention has been made in view of the foregoing circumstances, and an object thereof is to provide a thermostat failure diagnosis apparatus for an internal combustion engine, which can effectively conduct a failure diagnosis of a thermostat while an erroneous diagnosis is prevented.
In order to achieve the above object, a thermostat failure diagnosis apparatus of the present invention comprises cooling water temperature detection means for detecting a cooling water temperature of an internal combustion engine at an upstream side of a thermostat, detection means for detecting an intake air quantity of the internal combustion engine or a parameter related to the intake air quantity, and diagnosis means for detecting a failure of the thermostat on the basis of at least one of a time in which a rising quantity in the cooling water temperature reaches a predetermined value and a time in which the cooling water temperature rises to a predetermined temperature, in a case where a detection value detected by the detection means is equal to or higher than a predetermined value after starting of the internal combustion engine.
Alternatively, a thermostat failure diagnosis apparatus of the present invention comprises cooling water temperature detection means for detecting a cooling water temperature of an internal combustion engine at an upstream side of a thermostat, detection means for detecting a fuel injection quantity of the internal combustion engine or a parameter related to the fuel injection quantity, and diagnosis means for detecting a failure of the thermostat on the basis of at least one of a time in which a rising quantity in the cooling water temperature reaches a predetermined value and a time in which the cooling water temperature rises to a predetermined temperature, in a case where a detection value detected by the detection means is equal to or higher than a predetermined value after starting of the internal combustion engine.
In both cases, it is preferable that the failure diagnosis apparatus further comprises outside air temperature detection means for detecting an outside air temperature or a parameter related to the outside air temperature, and the diagnosis means permits failure diagnosis in a case where, after the starting of the engine, the cooling water temperature detected by the cooling water temperature detection means becomes equal to or higher than the outside air temperature detected by the outside air temperature detection means.
Besides, it is preferable that the diagnosis means conducts a failure diagnosis by comparing a predetermined time with at least one of the time in which the rising quantity in the cooling water temperature reaches the predetermined value and the time in which the cooling water temperature rises to the predetermined temperature, and the predetermined time is set based on the cooling water temperature detected by the cooling water temperature detection means.
According to such a failure diagnosis apparatus, when the generated heat quantity of the internal combustion engine is low so that an erroneous diagnosis may occur, the failure diagnosis is not made, and only in the state where the quantity of heat generated in the internal combustion engine is high to some degree, the failure diagnosis of the thermostat is made. Thus, the diagnosis having high reliability can be made while the occurrence of an erroneous diagnosis is suppressed.
Further, since a region where the failure diagnosis is made can be set in a region where the cooling water temperature easily rises, from the intake air quantity or the fuel injection quantity indicating considerably high correlation with output of the internal combustion engine, processing of the failure diagnosis can be effectively carried out, and a diagnosis time can also be made short.